In modern healthcare facilities, non-invasive imaging approaches are used for identifying, diagnosing, and treating diseases. One purpose to which such techniques are applied is the acquisition of images of the breast for use in identifying and diagnosing lesions or irregularities in the breast tissue.
In conventional mammography approaches, breast imaging may be implemented using radiographic techniques, such as by projecting X-rays through the breast tissue and reconstructing images based on the differential transmission of the X-rays through the tissue. Such approaches, however, may suffer from various detriments. For example, conventional radiographic imaging techniques are generally planar or two-dimensional (2D) in nature, limiting the ability of a diagnostician to visualize the results.
An alternative approach to conventional radiographic mammography involves an imaging technique known as tomosynthesis. In tomosynthesis X-ray attenuation data is obtained for a region of interest over an angular range (e.g., about typically 15 to 60 degrees) and this data is used to construct volumetric or generally three-dimensional (3D) reconstructions of the breast tissue. In general, tomosynthesis imaging exhibits good in-plane resolution with, potentially, poorer depth resolution. In this manner, tomosynthesis may be employed to non-invasively detect abnormalities in the breast tissue, such as lumps, fibroids, lesions, calcifications, and so forth. Such tomosynthesis systems are generally effective for detailed characterization of benign and cancerous structures such as calcifications and masses embedded in the breast tissue.
Another imaging approach for use in imaging breast tissue is ultrasound. An ultrasound imaging system uses an ultrasound probe for transmitting ultrasound signals into an object, such as the breast of the patient being imaged, and for receiving reflected ultrasound signals there from. The reflected ultrasound signals received by the ultrasound probe are generally indicative of boundary transitions between structures in the imaged region and may be used to reconstruct an image of the interior of the imaged anatomy. In general, ultrasound may exhibit good depth-resolution combined with a somewhat reduced in-plane resolution. Ultrasound imaging is useful as an alternate tool for diagnosis, such as for differentiating benign cysts and masses. In addition, ultrasound imaging may be used as a secondary screening tool in women with breasts that are dense. In dense breast tissue X-ray imaging is not as sensitive and the addition of ultrasound imaging has been shown to find more cancers.
A mammography system can have a compression plate to compress the breast against the image receptor which holds an X-ray detector. The mammography system can also contain an anti-scatter grid. The main purpose of the breast compression is to spread the tissue out and hold the tissue in place. For a tomosynthesis examination, the breast is positioned and compressed in the same way as for a mammogram but the X-ray tube moves in an arc around the breast and multiple X-ray images at different angles are taken. The information from the detector is sent to a computer, which produces a three-dimensional (3D) image of the breast. The X-ray dose for an individual tomosynthesis image is less than a regular mammogram, but the total dose for the examination is similar to that of a two-dimensional (2D) mammography examination. Using a flexible paddle for breast compression during mammography and tomosynthesis gives the patient the benefit of less pain and more comfort, and enables a potential for integration with breast ultrasound imaging. One of the big challenges however is that the top surface of the breast is not flat (e.g., angled, and/or non-planar) as when using a flat rigid paddle. This surface shape of the compressed breast has an impact on both the breast density estimation and the reconstruction of the 3D image.